The present invention relates to a carbon particulates cleaning device for collecting carbon particulates in exhaust gases discharged from an internal combustion engine and burning off the collected carbon particulates.
Recently, the diesel engine has been employed as an engine for a vehicle because of low fuel cost. However, the diesel engine discharges a larger amount of carbon particulates (smoke) as compared with the gasoline engine. Therefore, a particulates cleaning device for reducing the amount of discharged smoke is required.
Conventionally, such a particulates cleaning device has been composed of a heat resistant filter member which is formed of porous ceramic or metal fiber and is disposed in an exhaust gas passage of the diesel engine and an electric heater for heating and igniting carbon particulates collected by the filter member, which is disposed on or near the upstream end surface of the filter member. By this conventional device, carbon particulates collected in the upstream end portion of the filter member are ignited by the electric heater and the combustion flame is transmitted to the downstream portion of the filter member. As a result, all of the carbon particulates collected by the filter member are burnt off so that the filter member is regenerated.
However, the carbon particulates cleaning device of this type has a problem that the temperature of the exhaust gases is lower than the igniting temperature of carbon particulates while the vehicle runs under normal condition so that heat generated by the electric heater is taken away by the flowing exhaust gses when the volume of flowing exhaust gases is large, consequently, ignitability of carbon particulates is reduced.
In order to overcome this problem, such measures as to flow exhaust gases into a by-pass passage at the filter member regenerating time or to provide two filter members in parallel, which alternately collect carbon particulates while the inactive filter member is regenerated, have been taken.
However, in the former case, uncleaned exhaust gases are discharged from the by-pass passage at the filter member regenerating time and in the latter case, production cost and weight of the device increase.
In addition, in both cases, a diverter valve for changing the exhaust gas flow must be provided so that the structure of the device becomes complex.
Accordingly, one object of the present invention is to provide a carbon particulates cleaning device by which the carbon particulates collected by the filter member are surely ignited by consuming only a small amount of electric power and all of the collected particulates are burnt off without providing the above described by-pass passage or providing two filter members in parallel.